AP Biology Unit 6.1

Hershey & Chase (biomolecules: genes are made of DNA, not proteins)

The Hershey and Chase experiment demonstrated that DNA, not protein, is the genetic material in bacteriophages, using radioactive labeling to track the molecules.

Chargaff (DNA basepairing)

A pairs with T, C pairs with G

Meselson-Stahl (DNA replication is semi-conservative)

The Meselson-Stahl experiment demonstrated that DNA replication is semi-conservative, meaning that each new DNA molecule consists of one old strand and one newly synthesized strand.

Griffith Transformation Experiment (something is transforming cells, but what?)

The Griffith Transformation Experiment demonstrated that non-virulent bacteria could be transformed into virulent ones by exposure to heat-killed virulent bacteria, suggesting the presence of a 'transforming principle'.

Avery, MacLeod, & McCarty (DNA is the genetic information. It is transforming cells in the Griffith experiment.)

The Avery, MacLeod, & McCarty experiment established that DNA is the substance responsible for heredity and the 'transforming principle' identified in Griffith's experiment, proving that DNA carries genetic information.

nucleotides (phosphate, deoxyribose, nitrogen-containing base)

The basic building blocks of DNA, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base. They link together to form the DNA strand.

complementary basepairs (A:T, G:C)

Nucleotides that pair specifically in DNA, consisting of adenine pairing with thymine and guanine pairing with cytosine.

sugar-phosphate backbone

The sugar-phosphate backbone is the structural framework of nucleic acids, consisting of alternating sugar and phosphate groups that form the sides of the DNA or RNA ladder.

hydrogen bonds (hold the two strands together)

Weak attractions between base pairs in DNA.

double helix

structure of DNA

purines (A, G), pyrimidines (C, T, U in RNA)

Purines are double rings, and pyrimidines are single rings

antiparallel (if one strand runs 5’--> 3’, the other runs 3’--> 5’)

strands run in opposite directions

DNA’s charge

negative

DNA replication (occurs during S phase, so cells can divide!)

The process by which DNA makes a copy of itself during the S phase of the cell cycle, enabling cells to divide.

chromosomes in eukaryotes vs. prokaryotes

circular in prokaryotes, linear in eukaryotes

Origin of replication (Ori)

where the two strands are separated, opening a replication bubble

Replication fork

a Y-shaped region where new DNA strands are elongating

Template strand

parent/old strand

Daughter strand

newly synthesized DNA strand

DNA polymerase

enzymes that add nucleotides complementary to the template strands, and can only synthesize new DNA in 5’ to 3’ direction. They read the template strand from 3’ to 5’.

helicase

unwinds the DNA strands

ligase

joins fragments on lagging strand

topoisomerase

relaxes supercoiling in front of the replication fork

primase

synthesizes RNA primer to initiate DNA replication

RNA primer

a short, single-stranded RNA sequence synthesized by the enzyme primase to initiate DNA replication

leading strand

one strand continuously synthesized towards replication fork

lagging strand (discontinuous replication)

replication occurs away from replication fork

Okazaki fragments

a series of segments later joined by DNA ligase

semi-conservative replication

one strand of DNA serves as the template for a new strand of complementary DNA

telomeres

“caps” of long nonsense DNA sequences on eukaryotes - protect against DNA degradation

telomerase

Biotechnology

using DNA to make something fun/useful

PCR

synthetic replication of a target gene sequence, occurs outside of cell, allows scientists to clone a specific gene and amplify the amount of DNA they have for that gene)

denaturing

In high temperatures, hydrogen bonds between DNA strands break

annealing

lower temperature so primers can bind to outsides of target gene sequence on template strands

extension

increase temperature to ideal range for Taq polymerase, enzyme binds to primers and adds nucleotides to synthesize new strand of the gene

primers

a short, single-stranded nucleic acid sequence that serves as a necessary starting point for DNA synthesis and replication.

Master Mix

a pre-mixed, concentrated solution containing the essential ingredients required for a Polymerase Chain Reaction (PCR)

Taq polymerase

a thermostable DNA polymerase enzyme, essential in PCR for amplifying DNA sequences due to its ability to withstand high temperatures without denaturing, eliminating the need to add new enzymes every cycle.

Gel electrophoresis

separates molecules by size and charge (smaller move faster, more charge move faster)

Agarose gel

a widely used laboratory technique that separates DNA or RNA molecules based on size by applying an electric current to a porous agarose matrix

Electrophoresis buffer

maintain stable pH and provide conductivity for separating DNA, RNA, or proteins in gel electrophoresis

Ladder

size standard in electrophoresis, pre-made fragments of specific lengths

DNA sequencing

the laboratory process of determining the exact order of nucleotides—adenine (A), thymine (T), cytosine (C), and guanine (G)—within a DNA molecule

DNA fingerprinting

using electrophoresis to analyze DNA creates a unique pattern, like fingerprints, so this is the name of the technique

Restriction enzymes

proteins that cut DNA at specific sequences

Restriction/recognition site

where DNA is cut by restriction enzymes

Sticky ends

single-stranded, unpaired overhangs that facilitate easy, specific ligation to complementary strands

Blunt ends

straight cuts with no overhangs, allowing them to bind to any other blunt end regardless of sequence, though with lower efficiency